Optimized objective function for routing determination

ABSTRACT

Techniques are directed to determining a rank value associated with a first network node. An example method includes determining a second network node indicated as being a preferred parent network node for the first network node. A first rank value is processed to determine a second rank value, the first rank value corresponding to a path from the second network node to a destination network node, including rounding up the first rank value in a predetermined manner to at least a second next higher integral rank value than the first rank value, to determine the second rank value. The second rank value is processed with at least a third rank value to determine the rank value associated with the first network node, the third rank value associated with a path from one of a plurality of candidate parent network nodes, for the first network node, to the destination network node.

BACKGROUND

Communication networks, such as wireless mesh networks and other typesof networks, connect a variety of different devices that form a network.The different devices are known as network nodes. Network nodes in acommunication network are often configured such that network trafficfrom network nodes in the communication network may be communicatedthrough other network nodes along a path through the communicationnetwork, to a root network node or other destination network node.

Routing determination is a process of determining a path (such as anoptimal path) through the network nodes for the network traffic. Arouting determination may include applying one or more ObjectiveFunctions to one or more network nodes based on a Rank value associatedwith each of the one or more network nodes. An Objective Function is afunction that is meant to maximize or minimize a numerical value, suchas a Rank value. A Rank of a network node is an abstract numeric valuethat is an expression of a relative position of the network node withina network configuration, with regard to other network nodes includingneighboring network nodes. (Note that “Rank” and “Objective Function”are capitalized herein. These are terms that are utilized in variousrequests for comments (RFCs), as discussed later.)

The Rank of a particular network node may be based on or otherwiserelated to the Ranks of the neighboring network nodes and/or tocharacteristics of the links between the particular network node and itsneighboring network nodes. The characteristics of the links may beexhibited, for example, by metrics determined based on observingcommunications over the links. A particular network node may, forexample, set its own Rank using a process such as is described inSection 3.3 of RFC 6719, “The Minimum Rank with Hysteresis ObjectiveFunction,” March 2012. The Minimum Rank with Hysteresis ObjectiveFunction is known by its shortened name—MRHOF.

For example, the particular network node may have determined a preferredparent network node that the particular network node uses for relayingof communications between the particular network node and a destinationnetwork node, such as a root node of the network or of a portion of thenetwork. There may also be a set of network nodes that is a set ofcandidate parent network nodes, where each candidate network node is apossibility for relaying communications between the particular networknode and the destination network node based on a subsequent Rank androuting determination.

In some scenarios, even a slight increase in communication metric forcommunication between the particular network node and the preferredparent network node for the particular network node may result in anincrease in Rank for the particular network node. This may occur even ifthe slight increase in communication metric is merely transient. In somescenarios, this slight increase in communication metric, because itresults in increasing the Rank value advertised by the particularnetwork node, may further result in poisoning routes for childrennetwork nodes of the particular network node, that utilize theparticular network node to reach the destination network node. Anexample of poisoning is described at Section 8.2.2.5 of RFC 6550, “RPL:IPv6 Routing Protocol for Low-Power and Lossy Networks,” March 2012.

In these scenarios, the Rank of the particular network node may changefrequently. This may result in routes for the children network nodes,using the particular network node to relay communications with thedestination network node, being frequently poisoned. This is even thoughcommunication through the particular network node may still provide asatisfactory route to the destination network node and, in some cases,the only satisfactory route to the destination network node.

A route that is poisoned for this or other reasons may, as a result of asubsequent Rank and routing determination, be quickly reestablished,only to be poisoned again, and so on. Route establishment may utilize alot of network resources, including overhead for route establishmentmessaging between network nodes. The route establishment overhead canitself interfere with, or even overwhelm, regular network communicationsand/or other processing. It may be desirable to minimize poisoning ofroutes, including to limit such overhead.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is set forth with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different figures indicates similaror identical items.

FIG. 1 is a schematic diagram of an example network architecture.

FIG. 2 is a diagram showing details of an example network communicationdevice.

FIG. 3 is a diagram illustrating a portion of an Area Network, and isused to illustrate a process of Rank determination for a particularnetwork node.

FIG. 4 illustrates an example process for determining the Rank value tobe advertised by a particular network node.

FIG. 5 illustrates a second example process for determining the Rankvalue to be advertised by a particular network node.

DETAILED DESCRIPTION

As discussed above, some critical routing determination scenarios usingObjective Functions are prone to causing or contributing to networkinstability. The process of reestablishing a route to a destinationnetwork node may utilize handshake or other connectivity-establishingmessaging, as well as processing by the network nodes themselves. Suchmessaging and processing may be minimized or avoided if the networkinstability can be minimized or eliminated.

This disclosure describes techniques directed to Rank determination in amanner that may address network instability issues. In one examplemethod, a Rank value associated with a first network node is determined.The example method may include determining a second network node that isindicated as being a preferred parent network node for the first networknode. The method may further include processing a first Rank value todetermine a second Rank value, the first Rank value corresponding to apath from the second network node to a destination network node, theprocessing including rounding up the first Rank value in a predeterminedmanner to at least a second next higher integral Rank value than thefirst Rank value, to determine the second Rank value. The method mayfurther include processing the second Rank value along with at least athird Rank value to determine the Rank value associated with the firstnetwork node, the third Rank value associated with a path from one of aplurality of candidate parent network nodes, for the first network node,to the destination network node.

In some examples, the techniques may be implemented in the context of anadvanced metering infrastructure (AMI) of a utility communicationnetwork. However, the techniques described herein are not limited to usein a utility industry AMI. For example, the techniques may beimplemented in the context of Distribution Automation, Home EnergyManagement or any other type of wireless or wired network. Unlessspecifically described to the contrary, the techniques described hereinare applicable to any communications network, control network, and/oranother type of network or system. In one example, the techniques may beimplemented in the context of the Internet of Things (IoT).

Example Environment

FIG. 1 is a diagram illustrating an example networked environment orarchitecture 100. The architecture 100 includes multiple networkcommunication devices 102(1)-102(N) (collectively referred to as“network communication devices 102”) and a network communication device104, where N is any integer greater than or equal to 1. The networkcommunication devices 102 and the network communication device 104 maybe in communication with one another via an area network (AN) 106. Inthe example of FIG. 1, the network communication device 104 isimplemented as an edge device, which serves as a connection point of theAN 106 to one or more networks 108 (e.g., a backhaul network), such asthe Internet. The network communication device 104 may include, but isnot limited to, a field area router (FAR), a cellular relay, a cellularrouter, an edge router, a DODAG (Destination Oriented Directed AcyclicGraph) root, a root device or node of the AN 106, a combination of theforegoing, or the like. In this example, the network communicationdevice 104 relays communications from the AN 106 to a service provider110 via the one or more networks 108. The network communication device104 may be considered, for example, a root node of the AN 106. For atleast some purposes, the network communication device 104 may beconsidered a destination network node (at least an intermediatedestination) for communications from the network communications devices102.

As used herein, the term “area network” (AN) refers to a defined groupof devices that are in communication with one another via one or morewired or wireless links. Examples of area networks include, for example,local area networks (LANs), neighborhood area networks (NANs), personalarea networks (PANs), home area networks (HANs), field area networks(FANs), or the like. While only one AN 106 is shown in FIG. 1, inpractice, multiple ANs may exist and may collectively define a largernetwork, such as an advanced metering infrastructure (AMI) of a utilitycommunication network. At any given time, each individual device may bea member of a particular AN. Over time, however, devices may migratefrom one AN to another geographically proximate or overlapping AN basedon a variety of factors, such as respective loads on the ANs, batteryreserves, interference, or the like.

The term “link” refers to a direct communication path between twodevices (without passing through or being relayed by another device). Alink may be over a wired or wireless communication path. Each link mayrepresent a plurality of channels over which a device is able totransmit or receive data. Each of the plurality of channels may bedefined by a frequency range which is the same or different for each ofthe plurality of channels. In some instances, the plurality of channelscomprises Radio Frequency (RF) channels. The AN 106 may implement achannel hopping sequence, such that a channel may change over time.Although many examples discussed herein implement a plurality ofchannels as data channels, in some instances the plurality of channelsinclude a control channel that is designated for communicating messagesto specify a data channel to be utilized to transfer data. Transmissionson the control channel may be shorter relative to transmissions on thedata channels.

The AN 106 may comprise a mesh network, in which the networkcommunication devices relay data throughout the AN 106. Alternatively,or additionally, the AN 106 may comprise a star network, in which acentral device acts as a parent to one or more children devices.Further, in some instances the AN 106 may include a portion that isimplemented as a mesh network and a portion that is implemented as astar network. Moreover, in other instances the AN 106 may be implementedin whole or part by other types of networks, such as hub-and-spokenetworks, mobile networks, cellular networks, etc. In some instances, adevice may be able to communicate with multiple different types ofnetworks (e.g., a mesh network and a star network) at the same ordifferent times. For instance, if a device is unable to discover asuitable device in a mesh network mode, the device may attempt toconnect to a nearby star network, mobile data collection network, orcellular network. Regardless of the topology of the AN 106, individualnetwork communication devices may communicate by wireless (e.g., radiofrequency) and/or wired (e.g., power line communication, Ethernet,serial, etc.) connections.

In some instances, the service provider 110 comprises one or morecentral office systems that include a security service such asAuthentication, Authorization and Accounting (AAA) server, a networkregistration service such as Dynamic Host Configuration Protocol (DHCP)server, a network management service (NMS), a collection engine (CE), ameter data management system (in the utility context), a customerrelationship management system (in the sales context), a diagnosticsystem (in a manufacturing context), an inventory system (in a warehousecontext), a patient record system (in the healthcare context), a billingsystem, etc. Network communication devices may register or interact withsome or all of these one or more central office systems. In one example,the one or more central office systems may implement a meter datamanagement system to collect resource consumption data from the networkcommunication devices of the AN 106, process the resource consumptiondata, provide data regarding resource consumption to customers,utilities, and others, and/or perform a variety of other functionality.In other instances, the service provider 110 comprises other systems toimplement other functionality, such as web services, cloud services, andso on. In yet other instances, the service provider 110 may beimplemented as other types of devices, such as in the context of theInternet of Things (IoT) that allows a variety of devices to exchangedata.

The service provider 110 may be physically located in a single centrallocation, or it may be distributed at multiple different locations. Theservice provider 110 may be hosted privately by an entity administeringall or part of the communications network (e.g., a utility company, agovernmental body, distributor, a retailer, manufacturer, etc.), or maybe hosted in a cloud environment, or a combination of privately hostedand cloud hosted services.

As noted above, any of the network communication devices 102, thenetwork communication device 104, and/or the service provider 110 maycommunicate according to various modulation schemes that are availableto it and perform processing to determine and indicate a preferred linkto use for communication. Available modulation schemes may differ bymodulation type and/or by data rate.

For instance, the network communication device 102(3) may transmitand/or receive one or more communications/transmissions (e.g., ProtocolData Units (PDUs), such as bits, frames, packets, segments, etc.) withthe network communication device 102(1) and/or 102(2) and, based on themetric data about the communications, determine a preferred link to use.The network communication device 102(3) may maintain, at 114, Rank datafor other communication devices 102 that are available as a “parent”communication device to the network communication device 102(3) forrelaying communications between the network communication device 102(3)and a particular destination network node such as the networkcommunication device 104. Further, the network communication device102(3) or some other device may update its Rank value at 114 andadvertise the Rank value to other network communication devices 102,typically to neighboring network communication devices. The networkcommunication devices 102 that receive the Rank value may utilize theRank value to determine another network communication device to utilizeto relay communications to a destination network communication device.In some examples, the Rank data at 114 may be determined based on Rankvalues for a plurality of candidate network devices in a candidate setof parent network nodes for the communication device 102(3) and/or apath from the communication device 102(3) to the destinationcommunication device, through one of the plurality of candidate networkdevices.

Communication metric data may include a detected/measured value, acomputed value, or any other statistic, metric, or value related tocommunication. For example, communication metric data may indicate anumber of transmission attempts (e.g., a number of transmissions sent),a number of successful transmissions (e.g., a number of transmissionsthat are acknowledged by a receiving node), a number of unsuccessfultransmissions (e.g., calculated by subtracting a number of transmissionattempts by a number of acknowledgements), and so on. Further, in someexamples communication metric data includes an Expected TransmissionCount (ETX) metric and/or an Expected Transmission Time (ETT) metric, asdiscussed in further detail below.

In many instances, communication metric data may include data that isspecific to a particular modulation scheme and/or to a particular link(e.g., direct communication path between devices). To illustrate,communication metric data may indicate a number of successfultransmissions and a number of transmission attempts via a particularlink (between a first node and a second node) with a particularmodulation scheme.

An ETX metric may generally indicate an expected number of transmissionsrequired to successfully send a transmission to a device. The ETX metricmay be computed in a variety of manners. In one example, an ETX metricequals a total number of transmissions sent (e.g., transmissionattempts) over a number of successful transmissions (e.g., transmissionsacknowledged). In another example, an ETX metric equals 1/P, where P=PfxPr. Here, Pf corresponds to a probability that a transmissionsuccessfully arrives at a recipient, and Pr corresponds to a probabilitythat an acknowledgment transmission is successfully received by asender. Pf and Pr may be calculated according to the following formulas:

${Pf} = \frac{\begin{matrix}{{Number}\mspace{14mu}{of}\mspace{14mu}{{transmissions}\left( {{e.g.},{probes}} \right)}} \\{{received}\mspace{14mu}{by}\mspace{14mu} a\mspace{14mu}{{neighbor}\left( {{e.g.},{recipient}} \right)}}\end{matrix}}{{Number}\mspace{14mu}{of}\mspace{14mu}{{transmissions}\left( {{e.g.},{probes}} \right)}{sent}\mspace{14mu}{by}\mspace{14mu} a\mspace{14mu}{sender}}$$\quad{\Pr = \frac{\begin{matrix}{{Number}\mspace{14mu}{of}\mspace{14mu}{{transmissions}\left( {{e.g.},{probes}} \right)}} \\{{received}\mspace{14mu}{by}\mspace{14mu} a\mspace{14mu}{{sender}\left( {{e.g.},{recipient}} \right)}}\end{matrix}}{\begin{matrix}{{Number}\mspace{14mu}{of}\mspace{14mu}{{transmissions}\left( {{e.g.},{probes}} \right)}} \\{{sent}\mspace{14mu}{by}\mspace{14mu} a\mspace{14mu}{{neighbor}\left( {{e.g.},{recipient}} \right)}}\end{matrix}}}$

In some instances, such as where Pf and Pr cannot be computed separately(e.g., when the sender does not know the number of transmissions that areceiver sent to it), then the ETX metric may be estimated as in thefirst example above. That is, if Pf and Pr cannot be computed separatelydue to a lack of information, the ETX metric may correspond to a totalnumber of transmissions sent over a number of successful transmissions.

An ETT metric may generally indicate an expected time required tosuccessfully send a transmission to a device. In one example, the ETTmetric equals a time to transmit a transmission of a given sizemultiplied by the ETX metric.

Communication metric data may be used in a variety of manners. In someinstances, communication metric data is used to determine one or moreRank values. For example, a network communication device or other devicemay determine a Rank value based on ETX metrics for multiple modulationschemes that are available for the link. In particular, if a firstmodulation scheme that is supported by two network communication devicesis associated with a lower ETX metric than a second modulation schemethat is also supported by the two network communication devices, thefirst modulation scheme may be selected.

Example Network Communication Device

FIG. 2 is a diagram showing details of an example network communicationdevice 200, such as any of the network communication devices 102 or thenetwork communication device 104. The network communication device 200may comprise any type of network communication device (sometimesreferred to as a node, network node, computing device, or just device),such as a router (e.g., a field area router (FAR), a cellular router, anedge router, etc.), a utility meter (e.g., electricity, water, or gasmeter), a relay (e.g., a cellular relay), a repeater, a transformer, asensor, a switch, a control device, an encoder/receiver/transmitters(ERTs), an appliance, a personal computer (e.g., a desktop computer, alaptop computer, etc.), a mobile device (e.g., a smartphone, a tablet, apersonal digital assistant (PDA), an electronic reader device, etc.), awearable computer (e.g., a smart watch, an optical head-mounted display(OHMD), etc.), a server, an access point, a portable navigation device,a portable gaming device, a portable media player, a television, aset-top box, computer system(s) in an automobile (e.g., navigationsystem), a camera, a robot, a hologram system, a security system, ahome-based computer system (e.g., an intercom system, a home mediasystem, etc.), a projector, an automated teller machine (ATM), and soon.

In some instances, the network communication device 200 may comprise aFull Function Device (FFD), while in other instances the networkcommunication device 200 may comprise a Limited Function Device (LFD).An FFD may include more functionality/resources than an LFD, such asdifferent processing powers, processing capabilities, power reliance,hardware components, etc. In one example, an FFD is implemented as aMains Powered Device (MPD) that is connected to mains electricity (e.g.,electricity meters), while an LFD is implemented as a Battery PoweredDevice (BPD) that is not connected to mains electricity (e.g., a watermeter, gas meter, etc. that employs batteries). Since an MPD relies onmains power, the MPD may remain in an active state (e.g., a stateassociated with consuming more than a threshold amount of power).Meanwhile, since a BPD relies on battery power, the BPD may enter asleep state (e.g., a state associated with consuming less than athreshold amount of power) when the BPD is not communicating orotherwise performing operations. The BPD may use a communicationschedule to determine when to enter a sleep state and/or when to enteran active state. This may allow the BPD to conserve battery life. Insome instances, components of LFDs are lower power components than thecorresponding components of the FFDs.

As shown in FIG. 2, the example network communication device 200includes a processing unit 202, a transceiver(s) 204 (e.g., radio,modem, etc.), one or more metrology devices 206, and a power supply unit208. The processing unit 202 may include one or more processors 210 andmemory 212. The one or more processors 210 may comprise microprocessors,central processing units, graphics processing units, or other processorsusable to execute program instructions to implement the functionalitydescribed herein. Additionally, or alternatively, in some examples, someor all of the functions described may be performed in hardware, such asan application specific integrated circuit (ASIC), a gate array, orother hardware-based logic device.

The transceiver(s) 204 may comprise one or more hardware and/or softwareimplemented radios to provide two-way RF communication with othernetwork communication devices in the AN 106 and/or other devices via thenetwork 108. The transceiver(s) 204 may additionally or alternativelyinclude a modem to provide power line communication (PLC) communicationwith other network communication devices that are connected to anelectrical service grid.

In some instances, the transceiver(s) 204 may include differentcharacteristics depending on the type of device implementing thetransceiver(s) 204. For example, while both FFDs and LFDs havetransceivers, the specific transceivers used may be different. Toillustrate, an FFD transceiver may include a PLC modem while an LFDtransceiver may not because the LFD is not connected to an electricalpower line that could be used for PLC communications. Additionally, oralternatively, an LFD transceiver may employ a lower power RF radio tominimize energy consumption.

The metrology device(s) 206 may comprise physical hardware and/orsensors to measure consumption data of a resource (e.g., electricity,water, or gas) at a site of the meter. In the case of an electric meter,for example, the metrology device(s) 206 may include one or more Halleffect sensors, shunts, or the like. In the case of water and gasmeters, the metrology device(s) 206 may comprise various flow meters,pressure sensors, or the like. The metrology device(s) 206 may reportthe consumption data to a service provider via the transceiver(s) 204.The consumption data may be formatted and/or packetized in a manner orprotocol for transmission.

The power supply unit 208 may provide power to the network communicationdevice 200. In some instances, such as when the network communicationdevice 200 is implemented as an FFD, the power supply unit 208 comprisesa mains power connector that couples to an Alternating Current (AC) orDirect Current (DC) mains power line where the network communicationdevice 200 is installed. In other instances, such as when the networkcommunication device 200 is implemented as an LFD, the power supply unit208 comprises a battery, such as a Lithium Thionyl Chloride battery(e.g., a 3 volt battery having an internal impedance rated at 130 Ohms),a Lithium Manganese battery (e.g., a 3 volt battery having an internalimpedance rated at 15 Ohms), a Lithium Ion battery, a lead-acid battery,an alkaline battery, and so on.

The memory 212 may include an operating system (OS) 214 and one or moreapplications 216 that are executable by the one or more processors 210.The memory 212 may also include one or more metrology drivers 218configured to receive, interpret, and/or otherwise process metrologydata collected by the metrology device(s) 206. Additionally, oralternatively, one or more of the applications 216 may be configured toreceive and/or act on data collected by the metrology device(s) 206.

The memory 212 may also include one or more communication stacks 220. Insome examples, the communication stack(s) 220 may be configured toimplement a 6LowPAN protocol, an 802.15.4e (TDMA CSM/CA) protocol, an802.15.4-2015 protocol, 802.15.4g protocol, and/or another protocol.However, in other examples, other protocols may be used, depending onthe networks with which the device is intended to be compatible. Thecommunication stack(s) 220 describe the functionality and rulesgoverning how the network communication device 200 interacts with eachof the specified types of networks. For instance, the communicationstack(s) 220 may cause FFDs and LFDs to operate in ways that minimizethe battery consumption of LFDs when they are connected to these typesof networks.

As illustrated, the memory 212 may also include a portion 222 storingprogram instructions that, when executed by the one or more processors210, determines Rank values for the network communication device 200.The portion 222 of the memory 212 may also store the resultingdetermined Rank values, with the Rank values being updated from time totime.

The memory 212 of the network communication device 200 may includesoftware functionality configured as one or more “modules.” The modulesare intended to represent example divisions of software for purposes ofdiscussion, and they are not intended to represent any type ofrequirement or required method, manner or necessary organization.Accordingly, while various “modules” are discussed, their functionalityand/or similar functionality could be arranged differently (e.g.,combined into a fewer number of modules, broken into a larger number ofmodules, etc.).

The various memories described herein (e.g., the memory 212) areexamples of computer-readable media. Computer-readable media may takethe form of volatile memory, such as random-access memory (RAM) and/ornon-volatile memory, such as read only memory (ROM) or flash RAM.Computer-readable media devices include volatile and non-volatile,removable and non-removable media implemented in any method ortechnology for storage of information such as computer-readableinstructions, data structures, program modules, or other data forexecution by one or more processors of a computing device. Examples ofcomputer-readable media include, but are not limited to, phase changememory (PRAM), static random-access memory (SRAM), dynamic random-accessmemory (DRAM), other types of random-access memory (RAM), read-onlymemory (ROM), electrically erasable programmable read-only memory(EEPROM), flash memory or other memory technology, compact diskread-only memory (CD-ROM), digital versatile disks (DVD) or otheroptical storage, magnetic cassettes, magnetic tape, magnetic diskstorage or other magnetic storage devices, or any other non-transitorymedium that can be used to store information for access by a computingdevice. As defined herein, computer-readable media does not includetransitory media, such as modulated data signals and carrier waves,and/or signals.

While detailed examples of certain network communication devices aredescribed herein, it should be understood that those networkcommunication devices may include other components and/or be arrangeddifferently. As noted above, in some instances a network communicationdevice may include one or more processors and memory storing processorexecutable instructions to implement the functionalities they aredescribed as performing. Certain network communication devices mayadditionally or alternatively include one or more hardware components(e.g., application specific integrated circuits, field programmable gatearrays, systems on a chip, and the like) to implement some or all of thefunctionalities they are described as performing. Further, certainnetwork communication devices may include one or more network interfacesto send or receive data.

Example Processes

FIG. 3 is a diagram illustrating a portion 300 of an AN, such as the AN106 in FIG. 1. The FIG. 3 diagram is used to illustrate a process ofRank determination for a network node 302 that may be, for example, oneof the network devices 102 of the AN 106 in FIG. 1.

Rank may be thought of as a fixed-point number, where the position ofthe radix point between the integer part and the fractional part of thefixed-point number is determined by a parameter known asMinHopRankIncrease. See, e.g., RFC 6550. MinHopRankIncrease is theminimum increase in Rank between a network node and any of its candidateparent network nodes. When an Objective Function computes Rank, theObjective Function operates on the entire (e.g., 16-bit) Rank quantity,including both the integer part and the fractional part. However, insome examples, when Rank is compared for determination of parentrelationships, only the integer part of the Rank quantity is used.

An advertised Rank value for a particular network node may comprise ametric for communication between the particular network node and adestination network node. The metric may be, for example, anapproximation of an expected transmission count (ETX) as described inSection 3.4 of RFC 6719.

Referring to FIG. 3, a subset 304 of the network nodes includes anetwork node 306 and a network node 308. In the FIG. 3 example, thesubset 304 of the network nodes has been determined in some manner, suchas by observing and or otherwise obtaining metrics about communicationbetween the network nodes of the subset 304 and a destination networknode 310, to be the candidate parent network nodes for the particularnetwork node 302. For example, the network nodes of the subset 304 ofnetwork nodes may be candidates to relay communications between theparticular network node 302 and the destination network node 310, suchas in part directly linking to the particular network node 302.

As discussed above, MRHOF is designed to find the paths with thesmallest path cost to a destination network node. See, e.g., Section 3of RFC 6719. It does this while also attempting to minimize excessive“chum” in the network. Conceptually, the MRHOF uses two mechanisms.First, it finds the candidate parent network node with a minimum pathcost to the destination network node, which is the candidate parentnetwork node with the minimum Rank. Second, it switches to that minimumRank candidate parent network node, from a previously-preferred parentnetwork node, only if the minimum Rank path is shorter (in terms of pathcost) than the current path by at least a given threshold—referred to inRFC 6719 as “PARENT_SWITCH_THRESHOLD.” This second mechanism is called“hysteresis.”

As discussed above, there are some situations in which a route may bepoisoned such that the preferred parent network node is no longer used.For example, a particular network node, as a preferred parent networknode for various of its children network nodes, may poison routes forits children network nodes if the Rank of the particular network node isincreased. This may force the children network nodes of the particularnetwork node to reestablish a route to communicate with the destinationnetwork node. For example, referring to FIG. 3, the particular networknode 302 may be a preferred parent network node for the network node312, the network node 314, the network node 316 and the network node318. If the Rank of the particular network node 302 is increased, thenthe particular network node 302 may poison the route to the destinationnetwork node 310 from the network node 312, the network node 314, thenetwork node 316 and the network node 318, through the particularnetwork node 302.

Turning now specifically to the MRHOF process for Rank setting process,described at Section 3.3 of RFC 6719, this process describes that theRank for a particular network node (such as the particular network node302) is set as the maximum of:

-   -   1. The Rank calculated for the path through the preferred        parent.    -   2. The Rank of the member of the parent set with the highest        advertised Rank, rounded to the next higher integral Rank.    -   3. The largest calculated Rank among paths through the parent        set, minus MaxRankIncrease.        For item 1, the “path through the preferred parent” is the path        from the particular network node, through the preferred parent,        and to the destination network node. With continued reference to        the FIG. 3 example network 300, the “path through the preferred        parent” for Item 1 may be the path from the particular network        node 302 to the destination network node 310, through the one of        the network nodes in the subset 304 that is the preferred parent        network node of the particular network node 302. For item 2, the        parent set may be the subset 304. For item 3, in some examples,        MaxRankIncrease is set to zero.

It should be noted that, according to Section 3.3 of RFC 6719, a networknode's advertised Rank is set to the Rank of the preferred parent, plusthe value of a MinHopRankIncrease parameter, if the resulting value ishigher than the value determined using the items 1 to 3 described above.In some examples, the MinHopRankIncrease value is set to one for theintegral part of the Rank. For example, a Rank value may be two bytes,with the least significant byte being the fractional part of the Rankvalue and the most significant byte being the integral part of the Rankvalue. In such examples, where the MinHopRankIncrease value is set tointegral one, the MinHopRankIncrease value is 0x0100.

As discussed above, in some examples, an increase in the link costbetween a particular network node and the preferred parent network nodeof the particular network node may cause the advertised Rank value forthe particular network node to be increased. In some examples,increasing the advertised Rank value for a particular network node maycause the particular network node to poison the routes through theparticular network node used by children of the particular network node.This may happen even in situations where the increase in the link costbetween the particular network node and its preferred parent networknode is small.

In some examples, however, a modification to Item 1 may be utilized.With the modification to Item 1, increases in the link cost between theparticular network node and its preferred parent network node may bebetter tolerated with respect to routing. That is, with the modificationto Item 1, the smaller increases in the link cost may not cause theadvertised Rank value for the particular network node to be increased.As a result, the particular network node may not poison the routesthrough the particular network node used by children of the particularnetwork node. In some examples, the particular network node may be theonly possible parent node for children of the particular network node.Poisoning the route through the particular network node for children ofthe particular network node, in this situation, would result in thechildren having to reestablish a route through the particular networknode.

In one example, Item 1 is modified to be “The Rank of the preferredparent, rounded up to the second higher integral Rank.” The amount ofrounding in the modified Item 1 is an example, and other amounts ofrounding up are possible. With this modification to Item 1, the linkcost between the particular network node and its preferred parentnetwork node is no longer a consideration in determining the value forItem 1. Item 2, however, rounds up to only the first higher integralRank as specified by RFC 6179. By not considering the link cost from theparticular network node to its preferred parent network node in Item 1,this may minimize the situations in which the advertised Rank value ofthe particular network node increases. This thus may minimize thesituations in which routes from the children of the particular networknode, using the particular network node, are poisoned.

This may be useful for situations, for example, in which the particularnetwork node is the only candidate parent network node for the childrenof the particular network node, minimizing the poisoning/reestablishingcycle discussed above. This also may be useful in situations in whichthe particular network node is one of several candidate parent networknodes, since the link cost to a candidate parent network node would haveto go up substantially before Item 3, which considers the link cost,would overwhelm the Rank value determination for the particular networknode using Item 1 and Item 2. Furthermore, in some situations, the Rankvalue for a particular candidate network node may be determined based onItem 2 being the maximum determined Rank value, in which case there willbe no difference between the Rank value determined using Item 1 of theMRHOF and the modified Item 1.

Two examples using the modified Item 1 are now discussed, usinghexadecimal notation for all the values used and determined in theexamples. In the examples, the Rank value calculation using Items 1 and2 is illustrated, showing a first Rank value calculation and asubsequent Rank value calculation. Both the first and subsequent Rankvalue calculations are illustrated using the MHROF as described inSection 3.3 of RFC 6179 and using a modification to Item 1 of the MRHOF,as discussed above. As discussed above, the modification to Item 1 issuch that the Rank value of the preferred parent is rounded up to thesecond higher integral Rank. It should be recalled that, in any event,the Rank value determined for a particular network node is at leastMinHopRankIncrease greater than the Rank value for any candidate parentnetwork node. In the two examples, MinHopRankIncrease is assumed to be0x0100.

In Example 1, a particular network node has only one candidate parent(P1), which is the preferred parent network node. The first Rank valuecalculation for the particular network node results in an advertisedRank value of 0x0400.

Example 1

Standard MRHOF MRHOF modified Rank Rank of preferred Rounded parentrounded to Parent List Rank via to the next the second next Rank ETX (topreferred Higher Higher integral Parent (advertised) parent) parentintegral rank rank P1 0x020A 0x012C 0x0336 0x0300 0x0400For the subsequent Rank value calculation, the ETX to the preferredparent node network node increases only by one, from 0x012C to 0x012D.

P1 0x020A 0x012D 0x0337 0x300 0x0400As can be seen, using the MRHOF as modified, the result of thesubsequent Rank value calculation does not change, staying at 0x0400. Asa result, the advertised rank for the particular network node does notincrease from the first determination to the subsequent determination,and routes using the particular network node as a preferred parentnetwork node are not poisoned. Otherwise, using the standard MRHOF, theadvertised rank for the particular network node increases from the firstdetermination (0x0336) to the subsequent determination (0x0337), androutes using the particular network node as a preferred parent networknode may be poisoned.

In Example 2, the particular network node has two candidate parentnetwork nodes (P1 and P2), with P1 being the preferred parent networknode. For the standard MRHOF, Item 2 is calculated only for the parentnetwork node with the highest rank. The first Rank value calculation forthe particular network node results in an advertised Rank value of0x0400.

Example 2

Standard MRHOF MRHOF modified Rank Rank of preferred Rounded parentrounded to Parent List Rank via to the next the second next Rank ETX (topreferred Higher Higher integral Parent (advertised) parent) parentintegral rank. rank P1 0x020A 0x00C8 0x030A N/A 0x0400 (<0x0100) P20x020C 0x00FA N/A 0x0300 N/AFor the subsequent Rank value calculation, the ETX to the preferredparent network node P1 increases from 0x00C8 to 0x00B.

P1 0x020A 0x010B 0x0315 N/A 0x0400 P2 0x020C 0x00FA N/A 0x0300 N/ASimilar to Example 1, using the MRHOF as modified, the result of thesubsequent Rank value calculation does not change from 0x0400. As aresult, like with Example 1, the advertised rank for the particularnetwork node does not increase from the first determination to thesubsequent determination, and routes using the particular network nodeas a preferred parent network node are not poisoned. Otherwise, usingthe standard MRHOF, the advertised rank for the particular network nodeincreases from the first determination (0x030A) to the subsequentdetermination (0x0315).

FIG. 4 illustrates an example process 400 for employing techniquesdiscussed herein. For ease of illustration the process 400 may bedescribed as being performed by a device described herein, such as thenetwork communication device 200 and/or the service provider 110.However, the process 400 may be performed by other devices. Moreover,the devices may be used to perform other processes.

The process 400 (as well as each process described herein) isillustrated as a logical flow graph, each operation of which representsa sequence of operations that can be implemented in hardware, software,or a combination thereof. In the context of software, the operationsrepresent computer-readable instructions stored on one or morecomputer-readable storage media that, when executed by one or moreprocessors, perform the recited operations. Generally, computer-readableinstructions include routines, programs, objects, components, datastructures, and the like that perform particular functions or implementparticular abstract data types. In some contexts of hardware, theoperations may be implemented (e.g., performed) in whole or in part byhardware logic components. For example, and without limitation,illustrative types of hardware logic components that can be used includeField-programmable Gate Arrays (FPGAs), Application-specific IntegratedCircuits (ASICs), Application-specific Standard Products (ASSPs),System-on-a-chip systems (SOCs), Complex Programmable Logic Devices(CPLDs), etc. The order in which the operations are described is notintended to be construed as a limitation, and any number of thedescribed operations can be combined in any order and/or in parallel toimplement the process. Further, any number of the described operationsmay be omitted.

Referring to FIG. 4, the example process 400 is for determining the Rankvalue to be advertised by a particular network node, such as theparticular network node 302 in the FIG. 3 network 300. The particularnetwork node has a preferred parent network node and at least onecandidate parent network node. The process starts at 402. At each of404, 406 and 408, a tentative Rank value is determined for theparticular network node. In the FIG. 4 process, the particular networknode carries out the operations 404, 406 and 408 in parallel. In someexamples, the operations 404, 406 and 408 may be carried out in series,or in some combination of in series and in parallel.

At 404, the first tentative Rank value is determined by determining theRank value for the preferred parent network node, rounded to at leastthe second higher integral Rank. As discussed above, rounding to thesecond higher integral Rank is an example, and other amounts of roundingup (for example, beyond the second higher integral Rank) are possible.The operation at 404 may, for example, be as described above as themodified Item 1 of the Rank determination MRHOF processing.

At 406, the Rank of the candidate parent network node having the highestRank is determined, rounded to the next higher integral Rank. Forexample, referring to the FIG. 3 network 300, the candidate parentnetwork node having the highest Rank may be one of the candidate parentnetwork nodes in the subset 304 of network nodes. The operation at 406may, for example, be as described above as Item 2 of the Rankdetermination MRHOF processing.

At 408, the largest calculated Rank among paths through each parent ofthe candidate parent network device set is determined, minus theMaxRankIncrease parameter value. The paths are from the particularnetwork node, through each parent of the candidate parent network deviceset, to a destination node. The MaxRankIncrease parameter value may bezero or some non-zero value. The operation at 408 may, for example, beas described above at Item 3 of the Rank determination MRHOF processing.

At 410, the Rank value for the particular network node is set to themaximum of the Rank values determined at 404, 406 and 408. At 412, theRank value set for the particular network node at 410 is advertised,such as to children network nodes of the particular network node. Forexample, referring to the FIG. 3 network 300, the children network nodesof the particular network node 302 may be the network node 312, thenetwork node 314, the network node 316 and the network node 318. At 414,the process 400 ends.

Referring to FIG. 5, a second example process 500 is for determining theRank value to be advertised by a particular network node (a “firstnetwork node”), such as the particular network node 302 in the FIG. 3network 300. The particular network node has a preferred parent networknode and at least one candidate parent network node. The process startsat 502.

At 504, a first Rank value is processed to determine a second Rankvalue. The first Rank value corresponds to a path from a second networknode to a destination network node, where the second network node is thepreferred parent network node for the first network node. The processingincludes rounding up the first Rank value in a predetermined manner toat least a second next higher integral Rank value than the first Rankvalue, to determine the second Rank value. The operation 504 maycorrespond to the operation 404 in the FIG. 4 process 400, in someexamples.

At 506, the second Rank value is processed along with at least a thirdRank value to determine the Rank value associated with the first networknode. The third Rank value is associated with a path from one of aplurality of candidate parent network nodes, for the first network node,to the destination network node. For example, the third Rank value maybe determined by processing a fourth Rank value, corresponding to thepath from the one of the plurality of candidate parent network nodes,where the processing includes rounding up the fourth Rank value to anext higher integral Rank value. For example, the fourth Rank value maybe a highest Rank value of Rank values associated with each of theplurality of candidate parent network nodes. The operation 506 maycorrespond to the operation 406 in the FIG. 4 process 400, in someexamples.

At 508, the Rank value associated with the first network node isadvertised, such as to neighbor nodes of the first network node. At 510,the process 500 ends.

With the processes 400 and 500, network instability may be minimized,such as due to fewer changes to the advertised Rank value for aparticular network node. For example, this may contribute to minimizingpoisoning routes to children network nodes of the particular networknode, which may minimize overhead that would otherwise be utilized toreestablish poisoned routes.

CONCLUSION

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described. Rather,the specific features and acts are disclosed as exemplary forms ofimplementing the claims.

What is claimed is:
 1. A method to determine a rank value associatedwith a first network node, the rank value tolerant to increases in alink cost between the first network node and its preferred parentnetwork node with respect to routing, the method comprising: rounding upa first rank value in a predetermined manner to at least two integralrank values higher than the first rank value, wherein the first rankvalue corresponds to a path from a second network node to a destinationnetwork node and the second network node is indicated as being apreferred parent node for the first network node; determining a secondrank value based at least in part on the rounded-up first rank value;determining the rank value associated with the first network node basedat least in part on the second rank value along with at least a thirdrank value, the third rank value associated with a path from one of aplurality of candidate parent network nodes, for the first network node,to the destination network node; and advertising the rank valueassociated with the first network node to neighbor nodes of the firstnetwork node.
 2. The method of claim 1, wherein: the one of theplurality of candidate parent network nodes has a highest rank value ofa rank value associated with each other of the plurality of candidateparent network nodes.
 3. The method of claim 1, further comprising:determining the third rank value by rounding up a fourth rank value to anext higher integral rank value, the fourth rank value corresponding tothe path from the one of the plurality of candidate parent networknodes.
 4. The method of claim 3, wherein: the fourth rank value is ahighest rank value of rank values associated with each of the pluralityof candidate parent network nodes.
 5. The method of claim 3, wherein:the fourth rank value corresponds to at least one metric value for thepath from the one of the plurality of candidate parent network nodes,for the first network node, to the destination network node.
 6. Themethod of claim 5, wherein: the at least one metric value comprises anExpected Transmission Count (ETX) value.
 7. The method of claim 1,wherein: the second rank value corresponds to at least one metric valuefor the path from the second network node to the destination networknode.
 8. The method of claim 7, wherein: the at least one metric valuecomprises an Expected Transmission Count (ETX) value.
 9. A networkcommunication device, comprising: one or more processors; and memorycoupled to the one or more processors, the memory storing instructionsexecutable by the one or more processors to perform operations todetermine a rank value associated with a first network node, the rankvalue tolerant to increases in a link cost between the first networknode and its preferred parent network node with respect to routing, theoperations including: rounding up a first rank value in a predeterminedmanner to at least two integral rank values higher than the first rankvalue, wherein the first rank value corresponds to a path from a secondnetwork node to a destination network node and the second network nodeis indicated as being a preferred parent node for the first networknode; determining a second rank value based at least in part on therounded-up first rank value; determining the rank value associated withthe first network node based at least in part on the second rank valuealong with at least a third rank value, the third rank value associatedwith a path from one of a plurality of candidate parent network nodes,for the first network node, to the destination network node; andadvertising the rank value associated with the first network node toneighbor nodes of the first network node.
 10. The network communicationdevice of claim 9, wherein: the one of the plurality of candidate parentnetwork nodes has a highest rank value of a rank value associated witheach other of the plurality of candidate parent network nodes.
 11. Thenetwork communication device of claim 9, the operations furthercomprising: determining the third rank value by rounding up a fourthrank value to a next higher integral rank value, the fourth rank valuecorresponding to the path from the one of the plurality of candidateparent network nodes.
 12. The network communication device of claim 11,wherein: the fourth rank value is a highest rank value of rank valuesassociated with each of the plurality of candidate parent network nodes.13. The network communication device of claim 11, wherein: the fourthrank value corresponds to at least one metric value for the path fromthe one of the plurality of candidate parent network nodes, for thefirst network node, to the destination network node.
 14. The networkcommunication device of claim 9, wherein: the second rank valuecorresponds to at least one metric value for the path from the secondnetwork node to the destination network node.
 15. One or morecomputer-readable media storing instructions that, when executed by oneor more processors of a node, configure the node to perform operationsto determine a rank value associated with a first network node, the rankvalue tolerant to increases in a link cost between the first networknode and its preferred parent network node with respect to routing, theoperations comprising: rounding up a first rank value in a predeterminedmanner to at least two integral rank values higher than the first rankvalue, wherein the first rank value corresponds to a path from a secondnetwork node to a destination network node and the second network nodeis indicated as being a preferred parent node for the first networknode; determining a second rank value based at least in part on therounded-up first rank value; determining the rank value associated withthe first network node based at least in part on the second rank valuealong with at least a third rank value, the third rank value associatedwith a path from one of a plurality of candidate parent network nodes,for the first network node, to the destination network node; andadvertising the rank value associated with the first network node toneighbor nodes of the first network node.
 16. The one or morecomputer-readable media of claim 15, wherein: the one of the pluralityof candidate parent network nodes has a highest rank value of a rankvalue associated with each other of the plurality of candidate parentnetwork nodes.
 17. The one or more computer-readable media of claim 15,the operations further comprising: determining the third rank value byrounding up a fourth rank value to a next higher integral rank value,the fourth rank value corresponding to the path from the one of theplurality of candidate parent network nodes.
 18. The one or morecomputer-readable media of claim 17, wherein: the fourth rank value is ahighest rank value of rank values associated with each of the pluralityof candidate parent network nodes.
 19. The one or more computer-readablemedia of claim 17, wherein: the fourth rank value corresponds to atleast one metric value for the path from the one of the plurality ofcandidate parent network nodes, for the first network node, to thedestination network node.
 20. The one or more computer-readable media ofclaim 15, wherein: the second rank value corresponds to at least onemetric value for the path from the second network node to thedestination network node.